Process for stabilizing particulate alkali metal percarbonate

ABSTRACT

A process for stabilising particulate alkali metal percarbonate involves coating it with an aqueous solution, preferably concentrated, of a non-reducing oligomeric saccharide, preferably sucrose and especially together with an inorganic salt co-coating agent. The preferred co-coating agents are alkali metal silicate, sulphate, carbonate and carbonate chloride. Coated percarbonate is provided having an excellent combination of solubility, and stability, even with low amounts of coating agent.

The present invention relates to a process for stabilising particulatealkali metal percarbonate, and particularly to a coating processtherefor, to the particulate percarbonate having improved stability soproduced and to washing or bleaching compositions containing the same.

It is well known that particulate alkali metal percarbonates, includingsodium percarbonate in particular, can be used as bleach additives foraddition to detergent compositions, and as bleaching compounds indetergent powder mixtures, eg for domestic clothes washing or indishwashing compositions. In comparison with alkali metal perboratetetrahydrate, they have the advantage of dissolving more rapidly attemperatures in the range of 20° C. to 40° C., which is becomingincreasingly beneficial in view of the trend towards lower clotheswashing temperatures and the use of a bleach activator in conjunctionwith the bleach. Another advantage of percarbonates is that they areenvironmentally friendly. However, percarbonates have a knowndisadvantage of decomposing more quickly than sodium perboratetetrahydrate during storage in the powdered state, particularly ifstored in a damp atmosphere and in washing or detergent compositions.Moreover, other constituents of washing compositions such a alkalinebuilders are known to accelerate the rate of decomposition ofpercarbonates.

In order to improve the stability of percarbonates, and particularlysodium percarbonate, it has been proposed to treat the surface or thesurface layer of the percarbonate particles with a wide range ofmaterials, and in particular to coat or encapsulate the percarbonatewith those materials. A wide range of organic and/or polymer compoundssuch as paraffins, carboxylic acids, polyols, vinyl resins etc. andinorganic compounds such as silicates, borates, perborates, boric acids,carbonates, chlorides, sulphates and phosphates have been proposed ascoating materials. There remains, however, a continuing need to locatealternative or improved means for improving the stability ofpercarbonates.

In WO 95/18065, Solvay Interox has disclosed the use of complexes ofboric acid with polyols or hydroxycarboxylic acids as coating agents forpercarbonates, including, without any particular emphasis, complexes ofboric acid with saccharides. Research has shown that coating agentsincorporating boric acid or borates are amongst the most effectivecoating agents for stabilising percarbonate, including their complexeswith the polyol/hydroxycarboxylic acids, but some potential customersfor percarbonates dislike the presence of boron possibly because theyfear that its use in bleaching or washing compositions may be prohibitedor curtailed. Accordingly, it remains desirable for producers ofpercarbonate to continue to try to develop boron-free coating materials.

In the course of devising the instant invention, a number of the organicmaterials were tested which had been contemplated in WO 95/180650 incomplexes with the oxyboron compound. Amongst those materials,saccharides were tested and it was found that there was a substantialdifference between them in their performance at stabilising thepercarbonate, and particularly when the percarbonate is incorporated indetergent or washing compositions. In particular, it was found thatlactose, alternatively called milk-sugar, provided relatively poorstability when employed in a low proportion, even though it was allegedby Sunstar KK et al in JP 60116625 that a peroxide (5% potassiumpersulphate and 26% sodium percarbonate) coated with 15-25% milk sugarshowed good stability in an artificial teeth cleaning composition.

The present invention provides a process for stabilising a particulatealkali metal percarbonate by coating it with an effective amount of acoating material characterised in that the coating material comprisesnot more than 5% by weight, based on the coated material of anon-reducing oligomeric saccharide.

Herein by the term effective amount is meant an amount such that therate of decomposition of percarbonate is reduced in comparison with thecorresponding uncoated percarbonate, for example when stored in anatmosphere at 80% relative humidity and 32° C. in the presence of itsown weight of zeolite 4A as described hereinafter.

Herein, during the coating process, the coating material is brought intocontact with the particulate percarbonate, and especially suitably inthe form of an aqueous solution.

Without being bound by any theory, it is believed that the effectivenessof coatings obtained in the present process may be assisted by theability of solutions of the selected non-reducing oligomeric saccharidesto spread easily across the surface of the percarbonate and therebycreate a barrier or layer from even small amounts of coating agent thatprevents or reduces interaction between the percarbonate core and theenvironment, be it water vapor in the local atmosphere and/or otherparticulate materials in for example detergent compositions in whichpercarbonate is incorporated as a bleach. However, easy spreadability ofa solution of the coating a gent in practice is believed to contributeonly a part of the overall explanation as to how or why the selectedcoatings are so effective, because other sugars such as lactose arelikewise capable of spreading across the surface, but do not exhibit thesame performance.

The non-reducing oligomeric saccharide is preferably a disaccharide, andparticularly sucrose. It will be recognized that as employed herein, areference to sucrose includes the molecule itself and any polymericderivatives that are derivable during processes for applying a coatingto percarbonate. For example, during some processes for applying acoating and in most processes for drying a coated percarbonate, it isnormal practice to contact the percarbonate particles with a hot gas,which may encourage polymerization. For the avoidance of doubt, thederivatives of sucrose, if any, that arise during such coating or dryingprocesses are encompassed within the instant invention.

It will be recognized that the term oligomeric saccharide excludesstarch and like extremely high molecular weight materials.

The sucrose or other non-reducing oligomeric saccharide need notconstitute all the coating agent. Indeed, it is preferable for thecoating agent to further comprise at least one co-coating agent whichcan be a salt of a carboxylic or organophosphonic acid, but whichadvantageously is an inorganic salt. The salt may be employed as such orin the instance of for example carboxylic acids can be incorporated inthe solution employed for coating as the corresponding acid which isneutralized by contact with the percarbonate during the coating process.By so employing a co-agent, it is possible either to increase the totalcoating level without increasing the amount of sucrose or othernon-reducing oligomeric saccharide that is coated onto the percarbonateor to achieve the same total weight of coating but with a smallerproportion of sucrose or other non-reducing oligomeric saccharide. Insome preferred embodiments of the present invention, the non-reducingoligomeric saccharide provides a minor fraction of the total weight ofcoating agent.

It will also be understood that although oligomeric saccharides can beemployed in a small amount as a coating agent on an oxidizing agent suchas sodium percarbonate safely, ie as demonstrated by low heat emissionin a standard test, the use of significantly larger amounts result inmuch greater heat emission which demonstrates that the product is muchless safe than uncoated material. Accordingly, it is of practicalsignificance that the proportion of sucrose or other non-reducingoligomeric saccharide employed in the present invention be severelyrestricted. The potential oxidative interaction between sodiumpercarbonate and a oligomeric saccharide accordingly represents a majordifference between sodium percarbonate and other detergent ingredientslike zeolites as such or bearing absorbed additives which do not undergosuch oxidative interactions

It has been observed that in at least some methods of applying a coatingcontaining the non-reducing oligomeric saccharide, for example insolution onto a bed of percarbonate particles, there is a growingtendency for the resultant product to contain agglomerates as the weightproportion of the non-reducing oligomeric saccharide is increased aboveabout 2%. This tendency can be ameliorated by employing a co-coatingagent as described herein, and in any event, the agglomerates can bedisintegrated into constituent particles by gentle pressure, ie pressurethat is significantly below that at which compaction would be carriedout. It is a process advantage to avoid use of additional processingsteps, so that it is distinctly desirable to employ a co-coating agentand indeed. desirable to employ a mixture of the coating agents insteadof separate additions where more than one agent is used, though thelatter method remains viable, particularly if the additions occursimultaneously onto an agitated bed of particles.

The co-coating agent is often selected from inorganic salts, preferablyalkali metal or alkaline earth metal salts and more preferably an alkalior alkaline earth metal carbonate, sequicarbonate or silicate or salt ofa mineral acid, such as chloride, sulphate or phosphate. Within the termsilicates are encompassed materials which suitable obey the formulaM₂O.nSiO₂ in which M represents an alkali metal preferably sodium orammonium, and n is selected in the range of from 0.5 to 4. Within theterm phosphate, there are encompassed ortho, pyro and metaphosphates ormixtures thereof. Preferred selections of inorganic salts for employmentin combination with the non-reducing oligomeric saccharide includecarbonate, carbonate/chloride, carbonate/sulphatecarbonate/chloride/sulphate, sulphate, sulphate chloride and eithersilicate or any of the foregoing combinations together with silicate.The weight ratio of carbonate to respectively chloride or sulphate andsulphate to chloride is often chosen in the range of from 10:1 to 1:10in such combinations. When silicate is present, it often comprises from2 to 15% of the inorganic salts.

In many preferred embodiments of the present invention, the coatingapplied to the percarbonate comprises from 5 to 80 parts by of anon-reducing oligomeric saccharide, particularly sucrose together withrespectively 95 to 20 parts by weight in total of one or more inorganicsalts selected from an alkali metal carbonate, sequicarbonate,silicate-chloride, sulphate or phosphate, and especially from 10 to 60parts by weight of the non-reducing oligomeric saccharide together with90 to 40 parts by weight of said selected inorganic salt(s). Moredesirably, the inorganic-salts or combinations thereof are selected fromthe preferred selections listed above.

Especially desirable combinations of coating agents according to thepresent invention comprise from 15 to 50 parts by weight of sucrose inconjunction with 85 to 50 parts by weight of sulphate or silicate.

Instead of all or part of the inorganic salts, it is possible to employa salt and especially an alkali metal salt such as sodium or magnesiumof a carboxylic acid or hydroxycarboxylic acid. Suitable salts includetartrate, citrate, succinate, glutarate adipate and ascorbate, andpreferably the sodium, potassium or magnesium salts thereof Mixtures ofsuch salts can be used, as for example mixtures of succinate, glutarateand adipate.

It is highly desirable to select as co-coating agents those which arereadily water soluble in the range of ambient temperature to mildlyelevated, such as from about 10° C. to 40° C. or 60° C., whichencompasses temperatures usually encountered in cold steeping and lowtemperature machine washing or hand-washing laundry processes or incleansing of hard surfaces. Such co-coating agents include alkali metalsulphates, chlorides, phosphates and low molecular weight carboxylateslike tartrate, adipate or succinate. The choice of a soluble coagentwith sucrose or other oligomeric saccharide enables rapid dissolution ofthe percarbonate in use.

The coating agent or combination of coating agents of the presentinvention is advantageously employed in the form of an aqueous solution.In practice, the concentration of the coating agent, ie the total of thenon-reducing oligomeric saccharide and any co-coating agent, in theaqueous coating solution is at least half of, and preferably as close asis convenient to, its saturation concentration of the solution at theapplication temperature. In this way, only a comparatively small andpreferably at or near the smallest practicable quantity of water needsto be evaporated subsequently to produce dry percarbonate particles,thereby requiring a lesser or least heat input during the drying stage,but retaining the advantage of applying the coating agent in a solutionwhich can spread across the surface of the percarbonate. Theconcentration of coating agent in the aqueous coating solution isgenerally at least 15% by weight, preferably at least 20% by weight.Concentrations above or equal to approximately 25% by weight areparticularly advantageous and in many instances, the coating agents aresufficiently soluble that solutions containing between 30 and 35% byweight solute in 70 to 65% by weight water can be employed at a solutiontemperature in the region of 30 to 50° C. In some combinations, such aswith soluble silicates it is possible even to employ coating solutionscontaining from 35 to 43% by weight coating agent and the balance water(65 to 57%) at such temperatures. It will be recognized that the coatingagent solutions contemplated herein remain free flowing at applicationtemperatures, particularly when a mixture of non-reducing oligomericsaccharide and co-coating agent is employed, thereby assisting thepercarbonate particles to absorb at least a fraction of the solutionduring the process of applying the coating agent and to assist in therate of spreading of the solution across their surfaces. Suchfreeflowing capability of the solution, the excellent water solubilityof the coating agent or agents and also using a mixture of agents eachreduce a risk that oligomeric saccharide dust could be formedinadvertently in contact or in close proximity to a ready source ofoxygen.

The dissolution of the coating agent or its constituents can take placeconveniently at a temperature of from 15 to 95° C., and preferably from20 to 70° C.

It will be recognized that it is not necessary for all the coating agentconstituents to be dissolved in a single solution, and that eachconstituent or a sub-combination can be introduced separately, thoughsuch separate employment would tend to increase the amount of solutionneeded per weight unit of coating agent.

It will also be recognized that a slurry of the coating agents can beemployed instead of a solution, for example a suspension of particulateinorganic salt in a solution of the sucrose or other non-reducingoligomeric saccharide. This would enable a relatively large weight ofcoating to be applied in a single pass, but in practice usually requiressmall particulates of mean size below 100 microns to be processed.

The total quantity of coating agent used, including both non-reducingoligomeric saccharide, particularly sucrose, and any co-coating agents,usually represents 0.5 to 20% w/w of the coated percabonate Preferably,the total quantity is selected in the range of from 1 to 15% w/w and inmany instances from 2 to 10% of the coated percarbonate. In manypractical embodiments, the total weight of coating agent is selected inthe range of from 2 to 5%. The weight of sucrose or other non-reducingoligomeric saccharide is not more than 5%, is usually selected withinthe range of from 0.2 to 3%, in many instances from 0.5 to 2.5% and in anumber of favoured instances in the range of from 1% to 2% with thebalance of total coating agents weight being supplied by appropriateamounts of co-coating agent or agents, and in particular inorganicagents such as those indicated herein. The co-coating agent or mixtureof them, it will be seen, often provides a weight of from 0.5 to 6% ofcoating based on the weight of the coated material, and in manyinstances from 1 to 3%.

As a general indication, when a coating agent is applied by the samemethod, the extent to which percarbonate decomposition is amelioratedincreases as the thickness of the coat increases, though non-linearly.The selected weight of coating takes into account the manner of coating,the length of the period for which the resultant composition shouldremain stable, the environment in which the percarbonate will be used,such as the temperature and humidity of storage conditions and theproportion of relatively aggressive washing composition constituentslike zeolites, and the extent to which purchasers of the product willtolerate a reduction in the available oxygen (Avox) content of thepercarbonate.

The alkali metal percarbonate is preferably sodium percarbonate. In manyof the coated percarbonate products produced according to the presentinvention, the bulk density of the percarbonate so coated is selected inthe range of 0.8 to 1.2 kg/l. The rate of dissolution of percarbonatethat has been so coated is often acceptably rapid, when determinedaccording to a method adapted from international standard ISO 3123-1976.The time corresponding to a 90% dissolution of the sample ofpercarbonate coated according to the invention does generally not exceed2.5 minutes. The 90% dissolution time is the time taken for conductivityto achieve 90% of its final value after addition of coated sodiumpercarbonate to water at 15° C. and 2 g/l concentration. The method usedis adapted from ISO 3123-1976 for industrial perborates, the onlydifferences being the stirrer height that is 1 mm from the beaker bottomand a 2 liter beaker (internal height 183 mm, internal diameter 127 mm).

The particulate percarbonate that is suitable for coating in any processaccording to the present invention can have been prepared in any processknown as such for making an alkali metal percarbonate, e.g. by thedirect method, by fluid bed processes, or the so called wet processes inwhich percarbonate is crystallized from a saturated aqueous solutions,often by cooling and/or by optional addition of an alkali metal salt.

Advantageously, in a number of embodiments it is desirable to employ asfeedstock a percarbonate that does not contain a significant proportion,ie contains not more than 1% w/w of a halide such as chloride. Byselecting such a feedstock, obtainable from a suitably controlled andoperated fluidized bed or “wet bed” process, it is possible to obtain aparticularly beneficial combination of properties, part from theselected coating agent and part from the feedstock so as to achieve thebest result overall.

The percarbonate core particles which are coated by a process accordingto the present invention can incorporate various additives in a widerange of proportions and in accordance with known teachings and/orpractice. Such additives include, amongst others persalt stabilizers,crystal habit modifiers and salting out agents.

Persalt stabilizers can be selected from one or more of alkali metal andalkaline earth metal silicates, alkali metal and alkaline earthphosphates, magnesium compounds such as magnesium sulphate, chloride oroxide, organic complexing carboxylic acids and their salts, such asethylene diamine tetraacetic acid and/or salt, ordiethylenetriaminepentaacetic acid and/or salt and/or organicpolyphosphonate complexing agents such ashydroxyethylidenediphosphonate, and alkyleneaminopolymethylenephosphonates, includingethylenediaminetetramethylene phosphonic acid and/or salt,diethylenetriaminepentamethylenephosphonic acid and/or salt,cyclohexane-1,2-diaminetetramethylenephosphonic acid and/or salt.

In some highly desirable embodiments, the process of the presentinvention is employed to coat sodium percarbonate which contains a smallamount of up to about 0.5% w/w silicate distributed within its particlesand optionally a further small amount of up to about 0.5% of a silicateor silicate derivative on the surface of its particles, as a result ofthe timing and distribution of the addition of silicate in two stagesduring the crystallization and recovery of the particulate percarbonate,for example product that has been produced by amanufacturing/stabilising process described either in GB-A-1 553 505,published in the name of Interox Chemicals Limited or in GB-A-1 578 062,published in the name of Peroxid-Chemie GmbH

Crystal habit modifiers act on the morphology of the percarbonatecrystals and include organic polymeric compounds like polyacrylates andinorganic species such as polyphosphates eg sodium hexametaphosphate.

It will be understood that some agents can simultaneously provide anumber of different properties, such as stabilization and crystal habitmodification.

Salting out agents have conventionally been used in commercial processesthat have been employed in the last 60 years for the crystallization ofthe percarbonate from solution, and typically are highly water-solublealkali metal salts, such as sodium chloride, sodium sulphate, or sodiumhexametaphosphate. Alternatively, the percarbonate can be produced in acrystallisation process which does not employ a noncarbonate salting outagent, but takes advantage of the relative insolubility of sodiumpercarbonate compared with sodium carbonate in alkaline conditions andat temperatures in the region of about 10 to 25° C.

In some embodiments, the nature of a co-coating agent for percarbonateis selected to match or complement the salting out agent if any, that isemployed during its manufacture in a crystallisation process. Thus, ifthe sodium percarbonate is made with a chloride salting-out agent, it isoften convenient to employ a coating which contains sucrose pluschloride or chloride/carbonate. On the other hand, if a chloride-freecrystallisation process is used, it is convenient to employ a coatingwhich itself does not contain chloride or more than a very minorfraction of chloride providing no more than about 0.3% chloride on thepercarbonate.

The mean diameter of the percarbonate core particles that are coated bya process according to the present invention is at the discretion of theuser. The mean diameter is normally at least 100 μm and often notgreater than 2000 μm, and in many instances, the mean particle size(MPS) falls in the range of 250 to 1000 μm. However, it is particularlydesirable to employ percarbonate having an MPS in the region of fromabout 500 to 850 μm. In a number of advantageous embodiments of thepresent invention there is provided coated percarboate having an MPS ofat least 600 μm and preferably from about 700 to 850 μm.

The spread of percarbonate particles is at the discretion of thepercarbonate producer, but as a practical matter, and as has beenrealized for many years, it is advantageous for incorporation inparticulate detergent compositions for the percarbonate to avoid veryfine particles, such as particles of below about 100 or 150 μm, becausesuch particles are inherently more susceptible to environment-induceddecomposition—they present a much higher surface area to volume ratiothan larger particles and they therefore find it easier and quicker toabsorb moisture from the surrounding air. For many particulate detergentcompositions, it is also desirable to avoid or minimize particles largerthan about 1500 μm, to reduce potential problems of persalt/detergentparticle segregation. Thus, in many practical embodiments of the presentinvention, all or substantially all the percarbonate to be coated canpass through a sieve of 1500 μm and be retained on a sieve of 150 μm,and in at least some preferred. embodiments, at least 80% w/w of thepercarbonate is retained on a sieve of 350 μm and passes through a sieveof 1200 μm, desirably having an MPS of at least 600 μm and mostdesirably from 700 to 850 μm. In the context of its definition in EP451893, the percarbonate products having an MPS of over 600 μm and atleast 80% by weight between 350 and 1200 μm have a morphology index ofbelow 0.03, and when coated in accordance with the instant invention,yet still demonstrate an excellent rate of solubility, excellent in washperformance and excellent in pack stability.

The process according to the present invention by which percarbonateparticles are coated with the coating agent described above can compriseany method known in itself for contacting persalts with coating agent. Apreferred means for bringing the coating agent into contact with thepercarbonate comprises spraying an aqueous solution of the coating agentonto the percarbonate particles. It is particularly desirable for thepercarbonate particles to be kept in motion. Thus, a coating process ofthe present invention can desirably be carried out in a range ofapparatuses that can agitate particles, of which practical examplesinclude a fluid bed, a rotating plate, and a rotary mixer into each ofwhich it is convenient to spray the coating agent solution. During thecourse of the contact, the persalt tends to adsorb, and to some extentabsorb the coating agent solution and with simultaneous or subsequentevaporation of the solvent from the coating agent solution, a coating isdeposited around the percarbonate core.

It will be recognized that the invention coating process may beconducted in a single pass through the coating apparatus or in aplurality of passes, at the discretion of the user. A plurality ofpasses is particularly beneficial for application of a heavy coating inthat it reduces the amount of solvent that need be removed in each passand thus reduces or removes the risk of over-wetting the percarbonatebefore it is dried. A continuous or batch method can be used.

Contact of the coating agent solution with the percarbonate can becarried out at the same time and in the same vessel as evaporation ofsolvent from the solution and formation of the coating layer. The twosteps can alternatively be carried out separately in differentapparatus, which may in some cases be of the same type, eg both influidized beds or be of different types, such as the mixing step in arotary mixer and the evaporation step in a fluidized bed.

An apparatus such as a fluid bed is particularly suitable for carryingout simultaneous spraying and evaporation. In such an operation, thetemperature of the fluid bed is usually maintained in the range of 30 to95° C. and preferably 60 to 80° C.

One particularly advantageous process variation comprises contacting acharge of the percarbonate particles with a solution of the inventioncoating agent in a separate mixer, particularly a rotary mixer, anddrying the wetted percarbonate subsequently in a fluid bed. The solutioncan be introduced into the mixer by spraying or even via a coarse spraysuch as one or more nozzles. In this separate mixer variation, thetemperature in the mixer is often selected in the range of 10 to 60° C.and preferably 20 to 50° C. The advantage of employing a solutioncontaining sucrose is that it is able to spread readily across thepercarbonate particle surfaces within the mixer. Drying in the fluid bedis then often carried out at a temperature of 50 to 90° C. andpreferably of from 60 to 70° C.

The fluid bed employed herein either for a combined coating/dryingprocess or simply in the drying stage can be operated in accordance withknown procedures for coating/drying or simply drying persalts, as thecase may be. Thus, any non-reactive gas can be used as the fluidizinggas, including air in particular. The gas can be pre-dehumidified, ifdesired, and pre-heated to maintain the temperature of the fluid bed atthe desired value. It is also possible to use direct heating means forthe fluidized bed, such as a tube bundle placed within the fluid bed ora heated jacket around the bed. The upward airflow of fluidizing gas isregulated to maintain the percarbonate particles in an agitated state,ie not settling, but is not so great as to blow the particles, otherthan fines, out of the fluidizing vessel.

The aqueous coating solution and the percarbonate particles aregenerally brought into contact at a temperature within about 30° C. ofeach other and preferably within about 5° C. of each other.

The proportions of coating agent solution and percarbonate are chosen soas to leave, after drying, the desired weight of coating agent aroundthe percarbonate core. In practice, it is desirable to limit theaddition of solution to percarbonate in a fluid bed or mixer to amaximum water content of about 15% w/w so as to minimize or eliminatewetting out problems, more preferably to an amount selected in the rangeof about 3 to 12% w/w water and often from, about 6 to 12% w/w water. Itis normally desirable also to continue drying until the coatedpercarbonate has a moisture content of below about 1% w/w; such as inthe region of 0.1 to 0.7% w/w. The duration of the drying stage isusually determined by such practical considerations as, amongst others,the amount of coating agent solution being applied per unit weight ofpercarbonate, the residual content of moisture that will be tolerated;the temperature and moisture content of the influent fluidizing gas,whether additional heating is employed for the bed and the rate at whichthe gas flows through the bed. It will accordingly vary from apparatusto apparatus and be capable of control by a skilled person in the art ofcoating persalts with the aid of preliminary ranging trials.

It will naturally be recognized that the final form of a coating agenton percarbonate may change as a result of subsequent reaction orprocessing. Thus, for example, contact of a solution of an acidiccoating agent on the surface or in the surface layer of percarbonate ofan alkali, may result in the interaction of the acid with the alkali,and the drying stage can release water of hydration from some or allhydrated salts that might be expected to be present at ambienttemperature, provided that the drying temperature exceeds the transitiontemperature for such salts.

It will be seen that the present invention also provides coated alkalimetal and especially sodium percarbonate having advantageous properties.In some embodiments, by suitable selection of the coating agent andnature of the core percarbonate, the invention provides coated sodiumpercarbonate having 90% solubility in the solubility test hereinafterdescribed within 1.7 minutes and an Avox retention of at least 64% andpreferably at least 70% after 6 weeks storage in the stability testhereinafter described (set A). Such advantageous coated percarbonate isobtainable by coating percarbonate with a non-reducing oligomericsaccharide and optionally with a co-coating agent.

In preferred embodiments, the above identified combination of coatingproperties, namely rapid solubility and excellent storage stability isachieved with a coating that represents 2 to 5% by weight of the coatedproduct. This is especially advantageous, in that the benefit ofexcellent stability is achieved with the application of only a smallweight of coating agent. This is not only a cost advantage when comparedwith employing a larger amount of coating agent, but it also minimizesthe inevitable reduction in Avox content of the coated percarbonatecompared with the uncoated, feedstock percarbonate. By doing so, it ispossible to achieve in a number of preferred embodiments the benefits ofhigh stability and rapid solubility whilst retaining an Avox of above12.5% w/w, particularly above 13.5% and especially above 14%, dependingnaturally upon the Avox of the feedstock uncoated percarbonate.

Furthermore, in at least some of the particularly useful embodiments,the coated percarbonate having the desirable combination of solubilityand stability properties has a mean particle size of from 600 to 850 μmand preferably at least 700 μm. Such a mean particle size reduces thelikelihood of particle segregation of the percarbonate from otherconstituents of compact or ultra-compact or granulated “conventional”detergent compositions. Advantageously, therefore, the combination isachieved of large particle size with small amount of coating to obtainexcellent in pack stability and rapid dissolution.

Advantageously, it has been found that a number of preferred coatedpercarbonates according to the present invention have a heat emission at40° C. of below 4 μW/g and preferably below 1.5 μW/g in the beatemission test hereinafter described.

The present invention also relates to washing or bleaching compositionscontaining particulate coated sodium percarbonate, such as productaccording to the present invention described hereinabove and/or producedby the process according to the present invention hereinabove.

In many preferred washing compositions according to the presentinvention intended primarily for laundry washing, one or more of thecomposition components are selected within the following narrower bands:

percarbonate 2 to 40%, particularly 5 to 30%

surfactant 2 to 40%, particularly 5 to 25%

builder 1 to 60%, particularly 5 to 40%

diluent 1 to 70%, particularly 5 to 50%

additives 1 to 10% in total.

In many related bleach preparations, often intended for use inconjunction with detergent compositions containing little or no bleach,or as a bleach supplement to bleach containing compositions, such bleachpreparations contain

percarbonate 5 to 90%, particularly 20 to 50%

surfactant 0 to 20%, particularly 0.5 to 5%

builder 1 to 95%, particularly 30 to 80%

diluent 1 to 95%, particularly 30 to 80%

additives 0 to 20% in total, preferably 1 to 10%.

The surfactants for incorporation in solid laundry or bleachcompositions of the present invention can be selected from particulateor flaky anionic, cationic, non-ionic, zwitterionic, amphoteric andampholytic surfactants and can be either natural or synthetic soaps. Anumber of suitable surfactants are described in chapter 2 of SyntheticDetergents by A Davidsohn and B M Milwidsky (6th edition) published in1978 by George Godwin Ltd and John Wiley & Sons, incorporated herein byreference. Without limiting to these surfactants, representativesub-classes of anionic surfactants are carboxylic acid soaps, alkyl arylsulphonates, olefin sulphonates, linear alkane sulphonates,hydroxy-alkane sulphonates, long chain and OXO alcohol sulphates,sulphated glycerides, sulphated ethers, sulpho-succinates, alkanesulphonates, phosphate esters, sucrose esters and anionicfluorosurfactants; representative classes of cationic surfactantsinclude quaternary ammonium or quaternary pyridinium salts containing atleast one hydrophobic alkyl or aralkyl group; representative classes ofnonionic surfactants include condensates of a long chain alkanol witheither polyethylene oxides or with phenols, or condensates of long chaincarboxylic acids or amines or amides with polyethylene oxide, andrelated compounds in which the long chain moiety is condensed with analiphatic polyol such as sorbitol or condensation products of ethyleneand propylene oxides or fatty acid alkanolamides, polyalkylglucolides,glucosamides and fatty acid amine oxides; representative classes ofamphoteric/zwitterionic surfactants include sulphonium and phophoniumsurfactants, optionally substituted by an anionic solubilising group.The proportion of surfactant, expressed as a fraction of all thesurfactant present is often from {fraction (2/10)} to {fraction(8/10)}ths anionic, from 0 to {fraction (6/10)}ths non-ionic, and from 0to {fraction (3/10)}ths for the other surfactants.

Detergent builders that are suitable for inclusion in compositionsaccording to the present invention include specifically alkali metalphosphates, particularly tripolyphosphate but also tetrapyrophosphateand hexametaphosphate, especially the sodium salt of each, alkali metal,(preferably sodium) carbonates, alkali metal, (preferably sodium)borates, and siliceous builders including clays like bentonite, zeolitessuch as A, X, Y, AX and MAP zeolites (EP-A-O 552 053) and layeredsilicates such as the product available under the trade designationSKS6. The coatings achievable with the sucrose or like containingcoating agents of the present invention render sodium percarbonate thathas been so coated at higher levels particularly suited to incorporationin the relative aggressive detergent compositions, ie those containingaluminosiliceous builders. Mixtures of the zeolite builders either witheach other and/or with other siliceous and/or phosphate and or carbonateand/or clay builders can be employed in the instant inventioncompositions. Useful detergent compositions can also include organicchelating builders as nitrilotrisodium triacetate (NTA), EDTA, EDTMP andDTPMP. Such chelating builders can be employed in a relatively smallamount as an augmenting builder and peroxygen stabilizer, such as of 1to 10%.

The detergent compositionscan also contain diluents, in an amountusually of not more than about 50% w/w. Such diluents include sodium andmagnesium sulphate and are less favoured than previously bymanufacturers of detergent compositions, who in recent years havepromoted concentrated compositions and compositions having a higher bulkdensity.

Detergent compositions of the present invention can also contain othersubstances selected for dedicated purposes in detergent compositions,which in some instances are referred to collectively as detergentadditives. Among such additives, the following can be mentioned: persaltactivators, optical brighteners, foam inhibitors, enzymes, fadinginhibitors and antiredeposition agents, colorants, pH regulators. Suchaciditives for incorporation in persalt-containing detergentcompositions have been described in greater detail in Chapter 4 andexemplified in Chapter 7 of the aforementioned work by Davidsohn andMildwisky and are well known to skilled practitioners. Thus, forexample, the bleach activator is typically a compound which generates aperoxyacid or an anion thereof by reaction with the percarbonate and isemployed in a mole ratio of about 4:1 to 1:2 percarbonate: activator formonoactivating activators and proportionately for multi-activatingactivators. Peroxyacid-generating activators are usually N-acyl orO-acyl compounds and a peracid, often peracetic through to pernonanoicacid is generated by interaction between the compound and a perhydroxylanion liberated from the percarbonate on its dissolution. Activatorshave become regular constituents of washing compositions intended formachine washing at low temperatures. A non-exhaustive range ofactivators a1 to a20 described below can be employed herein.

(a1) carboxylic acid or mixed carboxylic acid/sulphonic acid anhydridessuch as benzoic anhydride, phthalic anhydride, bis(ethane sulphonic)acid, anhydride and benzene sulphonic acid/benzoic acid anhydride.

(a2) enol esters such as vinyl or isopropenyl acetate or benzoate ordivinyl adipate.

(a3) gem diesters such as ethylidene or isopropylidene diacetate ordibenzoate, or ethylidene benzoate acetate or heptanoate, orbis(ethylidene acetate) adipate or azelate.

(a4) sugar esters such as glucose pentacetate or lactose octacetate.

(a5) carbonic acid esters such as alkali metal salts ofpara(ethoxycarbonyloxy) benzoic acid or para(propyloxy carbonyloxy)benzene sulphonic acid.

(a6) N,N-diacylated amines, such as N,N,N′N′-tetraacetyl (methylene orethylene) diamine, N,N-diacetylaniline, N,N-diacetylmethylamine orN,N-diacetyl-p-toluidine.

(a7) Diacyiated hydantoins such as 1,3-diacetyl-5,5-dimethylhydantoin.

(a8) Acylated glycolurils, such as tetraacetylglycoluril.

(a9) N-alkyl-N-sulphonylcarbonamides, such as the compoundsN-methyl-N-mesylacetamide, N-methyl-N-mesyl-henzamide,N-methyl-N-mesyl-nitrobenzamide, andN-methyl-N-mesyl-p-methoxybenzamide.

(a10) N-acylated cyclic hydrazides, acylated thiazoles or urazoles, suchas monoacetylmaleic acid hydrazide.

(a11) Diacylated 2,5-diketopiperazines, such as1,4-diacetyl-2,5-diketopiperazine, 1,4-dipropionyl-2,5-diketopiperazineand 1,4-dipropionyl-3,6-dimethyl-2,5-diketopiperazine.

(a12) Acylation products of propylenediurea or2,2-dimethylpropylenediurea(2,4,6,8-tetraaza-bicyclo-(3,3,1)-nonane-3,7-dione, or its 9,9-dimethylderivative, especially the tetraacetyl- or thetetrapropionylpropylenediurea or their dimethyl derivatives.

(a13) O,N,N-trisubstituted hydroxylamines, such asO-benzoyl-N,N-succinyl-hydroxylamine,O-acetyl-N,N-succinyl-hydroxylamine,O-acetyl-N,N-phthaloyl-hydroxylamine,O-p-methoxybenzoyl-N,N-succinyl-hydroxylamine,O-p-nitrobenzoyl-N,N-succinyl-hydroxylamine andO,N,N-triacetylhydroxylamine.

(a14) N,N′-diacyl-sulphurylamides, such asN,N′-dimethyl-N,N′-diacetyl-sulphurylamide andN,N′-diethyl-N,N′-dipropionyl-sulphurylamide.

(a15) Sulphonyl halides such as p-(acetyl amino) phenyl sulphonvlchloride.

(a16) Azines such as diisocyanato-s-triazine or a halotriazine.

(a17) N-Sulphonylazoles.

(a18) N-acyl carboxylic imides such as N-acetyl caprolactam, N-acetyldiglycolimide, N-acetyl succinimide and N-acetyl phthalimide.

(a19) Mixed O-acyl, N-acyl compounds such asalpha-acetoxy-alpha-methyl-N,N′-diacetoxymalonamide orO-acetyl-N,N-diacetylethanolamine.

(a20) Salts of benzenesulphonic acid esters of carboxylic acids such assodium nonanoyloxybenzenesulphonate, sodium benzoyloxybenzenesulphonateor sodium isononanoyloxybenzenesulphonate.

The preferred activators include TAED, SNOBS, sodium isononoyloxybenzenesulphonate, TAGU and sugar esters. The weight ratio of percarbonate toactivator is often from 1:1 to 10:1.

Another type of activator for washing/bleaching compositions comprisescertain transition metal salts and/or complexes, for example certainmanganese, cobalt, and titanium complexes, sometimes employed inconjunction with a calcium promoter, as described in European PatentApplication-A-0 272 030. Commonly used optical brighteners includestilbene derivatives. Common antiredeposition agents includecarboxymethyl cellulose and polyvinyl pyrrolidone.

The washing and/or bleaching compositions can be employed for washingand or bleaching operations, such as for washing domestic laundry byhand or using machines employing either top loading or front loading,and using either long or short ratios of liquor to laundry. Suchmachines can be operated in accordance with currently describedoperation conditions for respectively persalt or persalt plus activatorcontaining compositions, including washing at cold soak temperatures, egfrom about 10 to 30° C., low temperature operation at from 30 to 60° C.(both of which preferably with bleach activator) or at high temperatureseg of about 60° C. up to boil wash. The detergent compositions can bedispensed in accordance with instructions on the container, such asdirect dispensing into the wash solution for hand washing, or into thelaundry before wetting for machine washing, or via a dispensing traythrough which wash water is flushed or from a dispensing ball or sachetplaced within the laundry.

By virtue of the excellent solubility of the invention coatedpercarbonate in aqueous wash solutions, and its excellent packstability, and especially of the best combinations tested, the inventioncoated percarbonate not only enables excellent stain removal ofbleachable stains to be effected, but it enables such performance to beretained to a substantial extent during a long period of time whilst thedetergent is distributed, purchased by the eventual end user and storedby the user.

In further variations on compositions containing percarbonate accordingto the instant invention, the compositions are employed for washingdishes. Such dishwasher compositions often comprise by weight:

percarbonate 2 to 30%, particularly 5 to 20%

surfactant 0.5 to 30%, particularly 1 to 25%

builder 1 to 80%, particularly 10 to 60%

additives 1 to 50% in total, preferably 5 to 30%.

In the dishwasher compositions, the surfictants are often selected fromranges of surfactants contemplated for laundry formulations; but in anamount and with a preference for low foaming surfactants and/or theaddition of sufficient foam suppressers to control to a minimum theextent of foaming within the dishwasher.

In the dishwasher compositions, the builders are normally selected fromwater soluble builders such as polycarboxylates, phosphates, silicates,carbonates and phosphonates such as those which have been describedherein briefly for laundry detergents. Polycarboxylates are amongst theespecially favoured builders. They can comprise acyclic, alicyclicaromatic or heterocylic carboxylic acids. Useful polycarboxylates areoften monomeric or oligomeric and can comprise, amongst others,dicarboxylic acids, tricarboxylic acids and tetracarboxylic acids. Theycan also be hydroxy-substituted. Suitable polycarboxylates can includealiphatic C4 to C6 α-ω dicarboxylates, optionally unsaturated, citrates,citraconates, carboxymethyloxysuccinates, oxypolycarboxylates, ethane orpropane tetacarboxylates and mellitate or pyromellitate. Other suitablepolycarboxylates include tetracarboxylate derivatives of cyclopentadieneor tetrahydrofuran, polycarboxylate derivatives of hexane andcarboxymethyl derivatives polyhydric alcohols, eg mannitol, xylitol orsorbitol.

The builder can desirably contain a small proportion (0.1 to 2%) ofcomplexing builders such as polyphosphonates, eghydroxyethanediphosphonate or polymethylenephosphonate derivatives ofamines or polyamines such as ethylenediamine tetramethylene phosphonateor cyclohexane-1,2-tetramethylene phosphonate or diethylenetriaminepentamethylene phosphonate, as such or in acid form.

Amongst the additives, it is preferable to employ a bleach activator,such as a1) to a20) described hereinabove in the ratio to percarbonateand weight proportions in the composition described for laundrycompositions. It is of practical benefit to employ a corrosion inhibitorin an amount of up to about 5%, preferably in addition to the variousphosphate builders which may also be present and which can inhibitcorrosion to a certain extent. Such additional corrosion inhibitorsinclude benzotriazole and its derivatives, aromatic mercarptans anddiols including lauryl mercaptan thiophenol, thionapthol, thioanthranoland thionalide. Other types of corrosion inhibitor include fattycarboxylic acids and their hydroxy-substituted counterparts, as such oras a watersoluble salt, hydroxyaromatic antioxidants and paraffin oils,preferably with molecular weight of about 350 to 600.

A further additive which can be present comprises an acidifier,preferably in an amount of 0.1 to 30% and particularly from 1 to 25%.The acidifier is often conveniently capable of acting as a builder whenintroduced into solution and is thus a carboxylic acid variation of theaforementioned carboxylate builders. Other suitable acidifiers includewater soluble monocarboxylic acids such as lactic acid. It is preferablefor the acidifier to be coated so as to delay release of the acidifieruntil a significant fraction of bleach activator has reacted with thepercarbonate, generating the more active peracid species. Suitablecoatings are often from about 3 to 10% by weight of poorly water-solublecompounds selected from hydrocarbon waxes, hydrogenated vegetable oils,fatty acids, amide derivatives or glycerides.

Coatings with a softening point around 40-50° C. are often of interest.

Dishwasher compositions containing the invention coated percarbonate arenormally provided in the form of granules or tablets obtained byconventional granulation of the powders preferably adding a percarbonategranule to preformed granules of the remaining detergent constituents orby compressing the constituents in a conventional method in a mouldpreferably in the presence of a typical tablet lubricant.

Processes for washing in automatic dishwashers are often conducted at atemperature in the region of about 40 to 70° C.

Certain embodiments of the present invention are described hereinafterin greater detail by way of example only.

In the Examples and Comparisons except where specifically indicatedcoated sodium percarbonate was obtained by the following general processand tested where indicated by the following test procedures.

Coating Process P1

A solution of defined coating agent constituent(s) was prepared bystirring a specified weight of the (or each) constituent in a specifiedweight of demineralised water and heating to approximately 40° C. ifnecessary until a clear solution without suspended solids was apparentto an experienced eye. A specified feedstock of particulate sodiumpercarbonate usually 1 kg was placed in a Lödige M5R™ mixer atlaboratory ambient temperature and sufficientsolution was poured slowlyonto the agitated particles to add the specified weight of coatingagent. The agitation was continued for a further 2-3 minutes to transferthe solution substantially evenly across the bed of particles. Theresultant damp particles were transferred into a laboratory scale(Aeromatic™ STREA 1) fluid bed drier in which they were fluidized anddried by an updraft of hot dry air having a temperature at inlet ofapproximately 70° C.-85° C. and maintaining a bed temperature of 65-75°C. for approximately 30 minutes. The particles were thereafter cooledbriefly by an updraft of cool air to a bed temperature of about 40° C.and were then available for a series of tests to determine theproperties of the coated products.

Feedstock Percarbonate Particles

F1 A feedstock obtained from a continuous wet process for precipitatingpercarbonate from aqueous solution in the presence of a chloridesalting-out agent and having mean particle size of 764 μm Avox of 13.2%and bulk density of 1.00.

F2 A second feedstock obtained from a continuous wet process forprecipitating percarbonate from aqueous solution in the presence of achloride salting-out agent and having mean particle size of 516 μm, andAvox of 13.65%.

F3 A third feedstock obtained from a continuous wet process forprecipitating percarbonate from aqueous solution in the presence of achloride salting-out agent and mean particle size of 489 μm, Avox of13.8% and bulk density of 1.01.

F4 A fourth feedstock obtained from a continuous wet process forprecipitating percarbonate from aqueous solution in the presence of achloride salting-out agent and having mean particle size of 465 μm, Avoxof 14.2% and bulk density of 0.99.

F5 feedstock obtained from a continuous wet process for precipitatingpercarbonate from aqueous solution in the absence of a chloridesalting-out agent having an Avox of 14.7%, mean particle size of 765 μmand bulk density of 0.97.

F6 A feedstock obtained from a continuous wet process, or precipitatingpercarbonate from aqueous solution in the absence of a chloridesalting-out agent having an Avox of 14.8%, mean particle size of 751 μmand bulk density of 1.04.

Particle Size Measurement

The particle size distribution was obtained by sieving the materialthrough a nest of 9 sieves with apertures ranging from 1400 down to 75μm. From the weight retained on each sieve, the weight fraction wasdetermined, and from the distribution, the mean particle size wascalculated.

Bulk Density

The free flowing bulk density of the products was measured placing asample in a cone of depth 60 mm, with top diameter 53 mm and basediameter 21 mm, the base being at a height of 20 cm above a work surfaceand allowed to flow under gravity into a collecting vessel on the worksurface. The contents of the vessel are carefully leveled off byhorizontal passage of a blade and weighed. The density is determined bycomparison with the known volume of the vessel.

Solubility

The solubility of the products listed in the Tables herein wasdetermined according to the method adapted from international standardISO 3123-1976 reported herein, by mixing the particulate product (2 g)with demineralised water (1000 g) maintained at 15° C. and theelectrical conductivity of the aqueous phase was monitored. Dissolutionof the percarbonate resulted in an increase in conductivity, and thetime taken to reach 90% of the maximum change was recorded in order toshow how fast or slow the products would dissolve. This is the test bywhich the solubility of the claimed products herein is judged.

Moisture Pick-up (32/80)

A 9 cm diameter petri dish with a 1 cm depth rim is weighed accuratelyon a 4 decimal place balance, (W1). A sample of dry sodium percarbonate(about 20 g) is placed on the petri dish which is gently agitated togenerate an even particulate layer across the base of the dish andreweighed on the same balance, (W2). The sample on the petri dish isstored in a room, about 3 m high, wide and long in an atmospheremaintained for a period of 24 hours at 32° C. by a thermostat controlledheater and at 80% Relative Humidity (RH) by introduction of a finedroplet water spray under the control of a humidity detector and weighedon the same balance, (W3). The samples are protected by a shield fromthe spray.

The moisture pick-up of the sodium percarbonate is calculated asfollows:${{Moisture}\quad {Pick}\quad {up}\quad \left( {g\text{/}{kg}} \right)} = \frac{1000 \times \left( {{W3} - {W2}} \right)}{\left( {{W2} - {W1}} \right)}$

The extent of moisture pick-up is indicative of the capability of the.product to extract moisture from its immediate environment, and thus ofthe stability of the product when exposed to humid conditions, forexample those which can be generated in detergent or bleach/additivecompositions containing substances like molecular sieves that arecapable of absorbing and releasing a significant proportion of moisture.

In the Tables, this is indicated by MPU.

Heat Emission

This was measured by transferring a sample of the percarbonate into amicrocalorimeter, model LKB 2277, also called a Thermal Activity Monitorwhich is marketed by Thermometric Limited, Sweden in which a temperatureof 40° C. is maintained. The heat from the sample over a standard periodof 16 hours is measured. In the Tables, this measurement is indicated byLKB40. This is the test by which the heat emission of the claimedproducts herein is judged.

A low reading indicates an intrinsically stable product, ie before theproduct is contacted with detergent composition or any other diluent.

Available Oxygen—Avox

Avox herein was measured by dissolving a weighed sample (about 0.2 g) inabout 100 mls of 10% w/w sulphuric acid and titrating the solutionagainst standard potassium permanganate solution.

Storage Stability

The storage stability of the products was tested in one of two generalmethods.

In a rapid method, 50 parts by weight of percarbonate was blended with50 parts by weight of a detergent constituent, specifically a detergentbuilder, Zeolite 4A powder obtained from Aldrich Chemicals to give aneven distribution and its available oxygen (Avox) measured. The blendwas stored in an open beaker housed in a constant environment chamber at32° C./80% relative humidity and samples were taken after specifiedperiods of storage and analyzed for residual Avox. A comparison of theAvox before and after storage is a demonstration of the stability of theproduct.

This method for determining percarbonate stability is referred to in theTables as “Avox Recovery Rapid”.

In a second method, usually conducted over periods of weeks, 15 parts byweight of percarbonate was blended with 85 parts by weight of one of thedetergent compositions indicated below and 50 g samples housed in smallsealed polyethylene coated cardboard cartons (Howarth Packaging) withmoisture permeability of 65.31 g m⁻² day⁻¹, measured at 32° C./80%relative humidity. The cartons were stored in a constant environmentchamber at 32° C./80% relative humidity and the Avox content afterstorage was compared with that before storage.

The reference percarbonate free compositions blended with the coatedpercarbonate (to obtain compositions according to the present invention)were as follows:

Reference detergent base A (P-free IEC base) Constituent % w/w Na linearalkylbenzene sulphonate 9.7 Ethoxylated tallow alcohol 5.2 Soap 3.6 Foaminhibitor 6.5 Zeolite 4A 32.5 Na carbonate 11.8 Na acrylate/maleatecopolymer 5.2 Na silicate (3.3:1) 3.4 CMC 1.3 Na EDTA 0.3 Stilbeneoptical brightener 0.3 Na sulphate 7.4 Proteolyte enzyme 0.6 Moisture12.2

The long term test for percarbonate, in which it was mixed withdetergent A and stored in small polyethylene coated cartons, is thestability test by which the claimed products is judged.

Reference Detergent B

Bleach-free detergent base of a commercially available laundry detergentcomposition containing zeolitie 4A builder

Reference Detergent C

Bleach-free detergent base of a second commercially available laundrydetergent composition containing zeolite 4A builder

The method of determining the stability of the percarbonate duringstorage mixed with one of the Reference Detergents is referred to inTables herein as “Avox Recovery Det A, B or C, as the case may be. Thestability is expressed in terms of the proportion of Avox remainingafter storage for 6 weeks, unless otherwise stated.

EXAMPLES 1 AND 2

In these Examples, a solution of sucrose (3009) in water (7009) wasprepared and employed in process P1 to provide coating of respectively1.8% and 3.0% by weight on feedstock F5.

TABLE 1 Ex 1 Ex 2 % Avox 14.3 14.2 Bulk Density g/cm³ 1.02 0.91Solubility min 1.3 1.5 LKB40 μW 4.3 2.7

From Table 1, it can be seen that products were obtained which each hadan excellent Avox and rate of solubility. The heat emission under thetest conditions, and although it was a coated product which led to anincrease in heat emission, showed an absolute figure within the rangewhich would have been observed for a typical uncoated conventionalChloride-salted out “wet route” percarbonate indicating that thecombination of salt-free feedstock with invention coating process is anadvantageous combination.

EXAMPLES 3, 4 and COMPARISONS C5 to C14

In these Examples and Comparisons, process P1 was followed employing103.1 g of the coating solutions summarized in Table 2 per kg offeedstock F1 to provide a total coating of 3% by weight coating agents.The coating solutions contained sodium sulphate and chloride in additionto either sucrose or comparison material.

TABLE 2 Ex/ Amount H₂O Na₂SO₄ NaCl Comp Organic agent G G g g 3 Sucrose12 70 16.32 1.68 4 Sucrose 18 70 10.88 1.12 C5 D-glucose 12 70 16.321.68 C6 D-glucose 18 70 10.88 1.12 C7 D-lactose 12 70 16.32 1.68 C8D-lactose 18 70 10.88 1.12 C9 L-ascorbate 12 70 16.32 1.68 C10L-ascorbate 18 70 10.88 1.12 C11 Mannitol 12 70 16.32 1.68 C13 Sorbitol12 70 16.32 1.68 C14 Sorbitol 18 70 10.88 1.12

The resultant coated products were found to be free-flowing powders andthe stability of the products in the presence of a detergent base wascompared in the standard method using Reference Detergent C. The resultsare summarized in Table 3

TABLE 3 Reference Detergent C 5 Avox recovery containing the product of6 weeks Ex 4 61 Comp 6 35 Comp 8 40 Comp 10 31 Comp 12 28 Comp 14 37 (4wk)

From Table 3 it can be seen that the products coated with the sucrosecontaining mixtures were markedly more stable than related productscontaining a similar amount of glucose, lactose, ascorbate, mannitol orsorbitol thereby demonstrating the outstanding nature of sucrose at evenlow amounts in the range of 1 to 2% w/w for coating percarbonate.

EXAMPLES 15 to 28

In these Examples a number of other coated percarbonate products wereobtained and tested which employed sucrose in combination with one ormore co-coating agents to coat the specified feedstock and to provide atotal coating amount shown in Table 4 below. NaG indicates sodiumgluconate; NaT disodium tartrate: NaC Trisiodium citrate;

TABLE 4 Coating solution composition constituent Weight Feed in g/kgCoat % Ex No. Stock Sucrose Water 3 Ex 15 F1 120 Na₂SO₄ 700 3 180 Ex 16F1 180 Na₂SO₄ 700 3 120 Ex 17 F2 60 Na₂SO₄ NaCl NaG 700 3 108.8 11.2 120Ex 18 F2 120 Na₂SO₄ NaCl NaG 700 3 108.8 11.2  60 Ex 19 F2 60 Na₂SO₄NaCl NaT 700 3 108.8 11.2 120 Ex 20 F2 120 Na₂SO₄ NaCl NaT 700 3 108.811.2  60 Ex 21 F2 60 Na₂SO₄ NaCl NaC 700 3 108.8 11.2 120 Ex 22 F2 120Na₂SO₄ NaCl NaC 700 3 108.8 11.2  60 Ex 23 F3 180 Na₂SO₄ MgCl₂ 700 3  6060 Ex 24 F3 180 CaCl₂ 700 3 120 Ex 25 F3 180 MgSO₄ NaCl 700 3  60 60 Ex26 F3 91 MgSO₄ 636 5 273 EX 27 F3 91 MgSO₄ 636 4 273 Ex 28 F3 300 MgSO₄490 3 210

The reasultant products were all found to have a bulk density in therange of 0.90 to 1.04 g/cm³. A number of the other properties of theproducts are summarized in Table 5 below.

TABLE 5 Avox Avox Recovery Recovery Ex No Avox MPS Solubility LKB40Rapid Det A 15 12.8 877 1.15 14.7 39 16 12.87 903 1.05 15.2 45 54 1713.17 545 1.10 9.9 18 13.22 474 1.20 7.1 19 13.35 624 1.10 5.4 20 13.39578 1.20 6.4 21 13.13 613 1.20 2.9 22 13.19 587 0.90 3.4 23 13.47 7450.90 5.3 34 55 24 13.47 639 0.90 12.5 32 42 25 13.47 612 0.80 3.6 38 4626 13.18 578 0.90 13.7 39 27 13.26 557 0.80 15.2 34 28 13.53 541 0.8018.0 31

By way of comparison, uncoated percarbonate feedstocks obtained from thesame process that produced feedstocks F2 to F4, retained on average inthe long term storage stability test herein, approximately 25 Avox after6 weeks storage mixed with Detergent Composition A ie in small boxes at32° C. and 80% relative humidity.

From Table 5 it can be seen that the products coated with a mixture ofsucrose and a selection of inorganic salts and carboxylate salts asco-coating agents showed a much improved solubility, and that the heatemission was lower in the presence of sodium salts and tended to behigher in the presence of magnesium or calcium salts. The coatedproducts were made in at least some Examples with little or no loss ofAvox. The invention coated products were significantly more stable thanthe uncoated feedstock percarbonate.

EXAMPLES 29 to 37

In these Examples sodium percarbonate is coated with a number ofcombinations of sucrose plus a co-coating agent as summarized in Table 6having properties summarized in Table 7. In subsequent Tables NaCMCindicates the sodium salt of carboxymethylcellulose silicate indicatessodium silicate having a mole ratio of Na₂O:SiO₂ of 1:2 and MgCindicates MgCl₂.2H₂O. In Examples 35 and 37 the coating was applied intwo layers with intermediate drying between the application of thecoating solutions.

TABLE 6 Ex Feed Coating solution composition constituent in g/kg WeightNo Stock Sucrose Water Coat % Ex 29 F6 180 Na₂SO₄ NaCl 700 3 108.8 11.2Ex 30 F5 178 MgCO₃ NaCMC Talc 693 3  40 10 79 Ex 31 F5 180 Na₂SO₄ 700 3120 Ex 32 F5 152.5 MgSO₄ 593 3 254.5 Ex 33 F5 180 Na₂SO₄ MgC 700 3  6060 Ex 34 F5 180 Na₂SO₄ 700 3 120 Ex 35 F5 Silicate 381.2 3 1^(st) 618.82^(nd) 180 Na₂SO₄ 700 2 120 Ex 36 F5 152.5 MgSO₄ 593 3 254.5 Ex 37 F5Silicate 381.2 4 1^(st) 618.8 2^(nd) 152.5 MgSO₄ 593 2 254.5

TABLE 7 Avox Recovery Ex No Avox MPS Solubility LKB40 Rapid 29 14.16 9931.2 4.0 61 30 14.28 917 1.4 1.0 58 31 14.17 856 1.1 1.2 61 32 14.4 6701.3 5.2 46 33 14.3 856 1.4 1.0 58 34 14.23 921 1.3 0.9 60 35 13.93 12081.7 3.9 67 36 14.37 826 1.3 6.3 56 37 13.95 786 2.2 4.1 59

From the results summarized in Table 7 it can he seen that many of theinvention coatings of the selected feedstock demonstrated a valuablecombination of properties including very high retained Avox aftercoating, fast solubility, low heat emission and improved stability evenwith a low level of coating agent.

EXAMPLES 38 to 51

In these Examples, yet further combinations of sucrose plus co-coatingagents were prepared and their properties summarized in respectivelyTables 8 and 9. In the Tables that follow NaP indicates sodium phosphateof formula Na₂HPO₄.2H₂O and STPP indicates sodium tripolyphosphate. *indicates that the result after 4 weeks storage is shown.

TABLE 8 Coating solution composition Feed constituent in g/kg Weight ExNo Stock Sucrose water Coat % Ex 38 F4 180 Silicate 572.5 3 247.5 Ex 39F4 120 Silicate 508.3 3 371.3 Ex 40 F4 173 Silicate Talc 602 3 190.334.6 Ex 41 F4 171.54 Silicate Glycerol 572.4 3 247.6 8.6 Ex 42 F4 180NaP 700 3 120 Ex 43 F4 150 NaP 700 3 150 Ex 44 F4 120 NaP 700 3 180 Ex45 F4 147.5 STPP NaCMC 700 3 147.5 4.9 Ex 46 F4 140 Na₂SO₄ 700 3 210 Ex47 F4 210 Na₂SO₄ MgC 650 3 70 70 Ex 48 F4 210 Na₂SO₄ 650 3 140 Ex 49 F4100 Na₂SO₄ 750 3 150 Ex 50 F4 150 Na₂SO₄ 750 3 100 Ex 51 F4 140 Na₂SO₄MgC 650 3 140 70

TABLE 9 Avox Avox Recovery Recovery Ex No Avox MPS Solubility LKB40Rapid Det A 38 13.72 545 1.1 39 43 56 39 13.65 574 0.7 5.3 55 47 4013.74 680 1.2 2.9 49 41 41 13.67 562 0.9 4.4 42 48 42 13.52 536 1.2 2.138  43* 43 13.65 619 1.2 2.5 31 44 13.82 558 1.2 2.0 45 13.32 587 1.22.9  52* 46 13.71 567 1.2 1.2 36 48 47 13.76 600 1.5 2.1 40 46 48 13.78589 1.25 1.2 35 50 49 13.80 669 1.25 1.6 40 49 50 13.79 623 1.2 1.6 3742 51 13.79 591 1.3 4.4 30 42

From the results summarized in Table 9 it can be seen that employing asfeedstock a conventionally salted out percarbonate it is still possibleto obtain coated products having fast solubility, an acceptable heatemission and improved stability.

EXAMPLES 52 to 55 and COMPARISONS C56 to C59

In these Examples and Comparisons products coated with the inventioncombination of coating agents are compared with known coating materials.The coating conditions and results are summarized in respectively Tables10 and 11. The results for C 59 are for the percarbonate feedstock F6alone.

TABLE 10 Coating solution composition Feed Constituent in g/kg Weight ExNo Stock Sucrose Water Coat % Ex 52 F6 180 Silicate 572 3 248 Ex 53 F6180 Silicate 572 3 248 Ex 54 F6 180 Na₂SO₄ 700 3 120 Ex 55 F6 180 Na₂SO₄381 3 120 Comp F6 Silicate 381 3 56 619 Comp F6 Na₃CO₃ Na₂SO₄ 750 3 57163 87 Comp F6 Na₂SO₄ 750 3 58 250

TABLE 11 Avox Avox Avox Avox Sol- Recov Recov Recov Recov Ex No ubilityLKB40 MPU Rapid Det A Det B Det C 52 1.3 4.0 5.6 76 78 58 71 53 1.4 3.65.5 72 75 57 71 54 1.2 1.0 5.3 71 73 60 64 55 1.7 1.1 5.7 74 68 60 64 C56 3.7 5.9 5.9 68 57 23 50 C 57 1.8 4.5 3.8 64 58 25 44 C 58 1.8 1.6 3.167 60 23 57 C 59 1.2 0 1.4 51 46 <5 26

From Table 11 it can be seen that the invention products demonstratedmarkedly superior stability to coated products which have hitherto beenrecognized as demonstrating one or more excellent properties andespecially in the presence of detergent compositions that are aggressivethat is to say cause comparatively rapid decomposition of sodiumpercarbonate. The demonstration of stability is noteworthy in that it isachieved at low levels of coating agent which enable the product todissolve at substantially the same rate as the uncoated feedstock andwithout increasing the moisture pick-up and heat emission rate tounacceptable levels. It can also be observed that the improvement instorage stability in the invention coated percarbonate is achieveddespite the fact that some of the comparison coated percarbonatesmanifested a lower moisture pick-up which would otherwise have beenexpected to accelerate decomposition.

What is claimed is:
 1. A process for stabilizing a particulate alkalimetal percarbonate by coating it with an amount of a coating materialwherein the coating material comprises not more than 5% by weight basedon the coated material of a non-reducing oligomeric saccharide.
 2. Aprocess according to claim 1 wherein the alkali metal percarbonate issodium percarbonate.
 3. A process according to claim 1 wherein thenon-reducing saccharide is sucrose.
 4. A process according to claim 1wherein the coating material contains a co-coating agent.
 5. A processaccording to claim 4 wherein the co-coating agent is an inorganic saltchosen from an alkali or alkaline earth metal carbonate, sequicarbonate,silicate, chloride, sulphate, phosphate, and mixtures thereof.
 6. Aprocess according to claim 5 wherein the coating agent comprises sucroseplus silicate or sulphate or a mixture of carbonate and chloride.
 7. Aprocess according to claim 1 wherein the coated percarbonate comprisesfrom 0.5 to 2.5% by weight of sucrose plus at least 0.5% by weightinorganic co-coating agent.
 8. A process according to claim 1 whereinthe coated alkali metal percarbonate comprises from 0.5 to 20% by weightof the coating agent.
 9. A process according to claim 1 wherein thecoating is applied by contacting an aqueous solution of the coatingagent with particulate percarbonate to form wetted particles andthereafter drying the wetted particles by agitation and contact with awater-removing gas.
 10. A process according to claim 9 wherein thesolution of coating agent is free from suspended co-coating agent.
 11. Aprocess according to claim 9 wherein the wetted percarbonate particlesare both agitated and fluidized by an updraft of the water-removing gas.12. A process according to claim 9 wherein the wetted particles arefluidized and dried at a bed temperature in the range of 30 to 90° C.13. A process according to claim 10 wherein the percarbonate particlesare contacted with the coating solution in a mixer, the temperature ofsolution in the mixer being from 10 to 60° C., and then dried in a fluidbed, the temperature of the fluid bed being from 50 to 90° C. 14.Particulate alkali metal percarbonate coated with an amount of a coatingmaterial comprising not more than 5% by weight based on the coatedmaterial of a non-reducing oligomeric saccharide, obtainable by aprocess according to claim
 1. 15. The coated percarbonate according toclaim 14 having 90% solubility within 1.7 minutes and an Avox retentionof at least 64% after 6 weeks storage.
 16. The coated percarbonateaccording to claim 14 wherein the coating represents 2 to 5% by weightof the coated product.
 17. The coated percarbonate according to claim 14wherein the percarbonate has a mean particle size of from 600 to 850 μm.18. The coated percarbonate according to claim 14 having a heat emissionat 40° C. of below 4 μW/g.
 19. The coated percarbonate according toclaim 17 containing at least 12.5% Avox.
 20. The washing or bleachingcomposition containing at least on washing agent and a coatedparticulate alkali metal percarbonate according to claim
 14. 21. Theprocess according to claim 7 wherein the coated percarbonate comprisesfrom 1 to 2% by weight of sucrose plus at least 1 to 6% by weightinorganic co-coating agent.
 22. The process according to claim 12wherein the bed temperature is in the range of 60 to 80° C.
 23. Theprocess according to claim 13 wherein the temperature of the fluid bedis from 60 to 80° C.
 24. The coated percarbonate according to claim 15having an Avox retention of at least 70% after six weeks storage. 25.The coated percarbonate according to claim 17 having a mean particlesize of at least 700 μm.
 26. The coated percarbonate according to claim18 having a heat emission at 40° C. of below 1.5 μW/g.
 27. The coatedpercarbonate according to claim 19 containing at least 14% Avox.